Several methods are known for making plastic eyeglass frames whose front portion is strengthened or reinforced interternally by a continuous metal blade member embedded in part of the thickness of the frame and extending around the glass-holding seats or windows and across the nose-bridging portion.
These earlier methods are not completely satisfactory. The reason for this is that in the earlier methods of embedding the metal blade in the plastic body, special and intricate techniques were required, along with the use of specifically designed tools, clamping devices and the like. These resulted in high cost, long machining times and low outputs.
In addition, eyeglass or spectacle frames could not be easily produced to accommodate adjustable and swinging nose-engaging elements, nor was it possible to provide eyeglass frames for a broad range of nose, sizes and shape.
Another disadvantage of the earlier systems was that they were unable to provide eyeglass frames of a high flexibility. As a result it was difficult to mount the lenses and to lock them in place.